Accuracy tests of radiation schemes used in hot Jupiter global circulation models

Abstract

The treatment of radiation transport in global circulation models (GCMs) is crucial for correctly describing Earth and exoplanet atmospheric dynamics processes. The two-stream approximation and correlated-k method are currently state-of-the-art approximations applied in both Earth and hot Jupiter GCM radiation schemes to facilitate the rapid calculation of fluxes and heating rates. Their accuracy have been tested extensively for Earth-like conditions, but verification of the methods' applicability to hot Jupiter-like conditions is lacking in the literature. We are adapting the UK Met Office GCM, the Unified Model (UM), for the study of hot Jupiters, and present in this work the adaptation of the Edwards-Slingo radiation scheme based on the two-stream approximation and the correlated-k method. We discuss the calculation of absorption coefficients from high-temperature line lists and highlight the large uncertainty in the pressure-broadened line widths. We compare fluxes and heating rates obtained with our adapted scheme to more accurate discrete ordinate (DO) line-by-line (LbL) calculations ignoring scattering effects. We find that, in most cases, errors stay below 10% for both heating rates and fluxes using ∼10 k-coefficients in each band and a diffusivity factor D = 1.66. The two-stream approximation and the correlated-k method both contribute non-negligibly to the total error. We also find that using band-averaged absorption coefficients, which have previously been used in radiative-hydrodynamical simulations of a hot Jupiter, may yield errors of ∼100%, and should thus be used with caution.

Dynamic mineral clouds on HD 189733b

“…Our gas phase opacities in Paper I used Planck mean opacities, which have been shown to have band averaged errors for the stellar heating rates (Amundsen et al 2014). This may be offset by the greyer opacity of the cloud particles, but regions where the gas opacity dominates (e.g.…”

Results from a set of three-dimensional numerical experiments of a hot Jupiter atmosphere

“…(see Mayne et al 2014a, for details). Amundsen et al (2016) features models using only the 'full' equations but incorporating a two-stream, dual band, correlated-k radiative transfer scheme, which has previously been tested in Amundsen et al (2014Amundsen et al ( , 2017, alongside minor updates in the treatment of diffusion and minor parameter changes (hereafter termed RT, referring to 'Radiative Transfer', simulation). The model uses SI units, and these are adopted throughout this work.…”

“…Therefore, although much progress has been made (and much more can yet be made) using 1D models, 3D models are required to truly unpick the observations, and extract robust physical meaning. E-mail: nathan@astro.ex.ac.uk Several GCMs (or similar models) with varying levels of sophistication have been applied to hot Jupiters (see for example Cooper & Showman 2005;Cho et al 2008;Menou & Rauscher 2009;Rauscher & Menou 2010;Heng et al 2011;Dobbs-Dixon & Agol 2013;Parmentier et al 2013;Showman et al 2015;Helling et al 2016;Kataria et al 2016;Lee et al 2016), including our own adaptation of the Met Office GCM termed the Unified Model (UM) (Mayne et al 2014a,b;Amundsen et al 2014;Helling et al 2016;Amundsen et al 2016Amundsen et al , 2017Boutle et al 2017). However, much of the progress has been driven by application of a single GCM, the SPARC/MITgcm.…”

Transmission spectral properties of clouds for hot Jupiter exoplanets

“…Figures 2 and 7 show that these condensates are highly scattering well into the infrared following a Rayleigh slope to ∼10 µm. Vibrational modes are unlikely McCullough et al 2014) compared to hydrocarbon condensates and gaseous CH 4 (Yurchenko & Tennyson 2014;Amundsen et al 2014) and C 2 H 4 (Rothman et al 2009;Sharp & Burrows 2007). to be observed in hot Jupiter transmission spectra due to the obscuring molecular features, similar to sulphur-bearing condensate species. However, there is potential for chloride clouds to be inferred in cooler exoplanetary atmospheres where strong Rayleigh scattering is observed in the optical and there is no evidence for atomic gaseous Na or K in the optical spectra, suggesting that the species may have condensed out of the atmosphere forming clouds of liquid or solid particles.…”

“…Figure 8 shows the transmission spectrum of HD 189733b with the considered hydrocarbon species as well as the expected transmission spectrum for gaseous CH 4 at solar abundance. The opacities for gaseous CH 4 are calculated from the new ExoMol line list (Yurchenko & Tennyson 2014), with the line width parameters as in Amundsen et al (2014). It can be seen that the gaseous CH 4 transmission spectral features overlap considerably with that of the hydrocarbon condensate cloud spectra, specifically at the 3 µm range where the vibrational mode of the C−H bond is responsible for the absorption feature.…”